Box of death's dirt

You come into possession of an old box. Inside are several glass vials filled
with dirt, dust and tiny bits of gravel or cement. The vials are labeled with
places and dates such as “Port Chicago 7/17/44?, “Halifax 7/6/17? and
“Guernica 7/17/36?. A trip to the library confirms that all are dates of massive
loss of life in explosions. A few days later a package arrives with no return address.

Inside is an empty vial labeled with your home town and next week’s date.